1. Field of the Invention
This invention relates to a silicon semiconductor substrate and a method for the production thereof. More particularly, the invention relates to a silicon semiconductor substrate of a void type product possessing a high gettering layer directly below a defect free zone thereof, and a method for the production thereof.
2. The Prior Art
For improving the gettering effect of a semiconductor substrate, a silicon wafer cut out of a silicon single crystal formed by pulling from a silicon melt according to the Czochralski method has been known from Japanese Patent No. JP-A-06-252,154. This document describes a silicon wafer having the following characteristics: The surface layer part of the mirror face thereof has an interstitial oxygen concentration of not more than 2×1017 atoms/cm3; the thickness thereof over a depth of not less than 10 μm from the surface of the mirror face forms a defect free zone; the defect free zone contains such minute defects as oxygen precipitates at a density of not more than 105 pieces/cm3; the region thereof deeper than the defect free zone is possessed of an internal gettering layer having minute defects formed therein at a density of not less than 108 pieces/cm3; and the rear side of the mirror face thereof is not possessed of an external gettering layer.
Regarding both the improvement in the defect-free zone of a void type defect and the improvement in the gettering effect, a silicon single crystal wafer obtained by slicing a silicon single crystal ingot grown by being doped with nitrogen according to the Czochralski method has been shown in Japanese Patent No. JP-A-2000-211995. This patent refers to a silicon single crystal wafer having the following characteristics: The silicon single crystal wafer has a defect-free zone (hereinafter called a “denuded zone”, DZ) with a depth in the range of 2–12 μm after the gettering heat treatment or after the heat treatment performed for the production of a device and has internal minute defects at a density in the range of 1×108–2×1010 pieces/cm3.
The former invention suggests nothing about the addition of nitrogen and discloses absolutely nothing about the denuded zone of a void type defect. The latter invention suggests nothing about the optimization of the nitrogen concentration and the cooling rate of the silicon single crystal being pulled at a temperature range of 1100° C. (hereinafter referred to simply as “cooling rate”) to be attained by controlling both the void type crystal defects and the depth of the oxygen precipitate type defect from the surface.
Specifically, the prior art attains an addition to the depth of the defect-free zone of void type crystal defects by elongating the duration of an annealing operation or heightening the annealing temperature. This approach, however, is at a disadvantage in promoting the external diffusion of oxygen, further increasing the width of the defect-free zone of an oxygen precipitate, and dissolving the oxygen precipitate and consequently weakening the gettering effect.